This invention relates to laminated magnetic cores produced by winding up thin metal tape, and to a method of manufacturing these.
Recently, amorphous thin metal magnetic tapes have attracted attention as materials for constructing the magnetic cores of transformers and magnetic cores of magnetic amplifiers, on account of their very superior magnetic properties.
Such magnetic cores fabricated from amorphous thin metal tapes are produced by winding up thin metal tape into the required shape. Depending on the application, such magnetic cores may be toroidal cores or cut cores.
For example, cut cores employing amorphous thin metal tapes are manufactured as follows.
The amorphous thin metal tape is first laminated by winding up to the desired shape on a winding jig. Next, it is subjected to heat treatment below the crystallization temperature, in order to remove strain in the amorphous thin metal tape and to obtain good magnetic properties. It is then cut at the appropriate places to produce a cut core shape.
However, when such cutting is carried out, if the layers in the wound-up body were not fixed, the cutting produces distortion of the thin tape at the cut face, or loss of the shape of the wound up body. The gaps between the layers of the wound-up body are therefore impregnated with an epoxy resin or the like, and the cutting is only performed after the wound-up body has been fixed by hardening the resin.
However, if the amorphous thin metal tape is fixed by resin impregnation as described above, the internal stress of the amorphous thin metal tape is increased due to distortion of the amorphous thin metal tape by contracting forces generated when the resin is hardened. This increases the core loss of the magnetic core that is obtained. There is a particular problem with epoxy resin due to its large contraction rate on hardening.
Accordingly, countermeasures are adopted, such as decreasing the contraction rate on hardening by changing the type of resin used for the impregnation. Some degree of success has been obtained with amorphous thin metal tapes of comparatively small width. However, in the case of magnetic cores employing amorphous thin metal tape of larger width, sufficient reduction of distortion has still not been obtained. Reducing the core loss of wound magnetic cores is therefore considered an urgent task.
As described above, magnetic cores employing a wound-up body consisting of amorphous thin metal tape are subject to the problem of increased core loss, caused by forces of contraction, etc., that are produced during hardening of the impregnating resin. Furthermore, there is the problem that low core loss, in particular when wide amorphous thin metal tape is used, cannot be obtained simply by decreasing the force of contraction of the resin.